Field of the Invention
The present invention relates to an electronic circuit that has an electromagnetic band gap structure.
Description of the Related Art
In recent years, review has been underway on the use of metamaterials in the field of electromagnetic waves in antennas, microwave circuits, and the like. A metamaterial is, in a broad sense, an artificial substance that does not exist in the natural world, and is classified into one of three types, namely a left-handed material whose dielectric constant and magnetic permeability are simultaneously negative, a material having either a negative dielectric constant or a negative magnetic permeability, and a right-handed material whose dielectric constant and magnetic permeability are simultaneously positive. Among these, it is known that a material with either a negative dielectric constant or a negative magnetic permeability has an electromagnetic band gap (EBG) property of stopping the propagation of electromagnetic waves.
It is known that by manipulating the substance, shape, and alignment of unit elements, a material having the EBG property can be realized using materials that exist in the natural world. A periodic structure that has an EBG property arising from unit elements will be called an EBG structure hereinafter. In electronic circuits, an EBG structure can be used as a band-stop filter for cutting off a specific frequency band, such as electromagnetic noise that causes unnecessary radiation to be emitted from the substrate on which electronic components are mounted.
In general, change of the cut-off frequency is not easy due to the EBG structure being formed in the substrate or on the substrate. Also, there is known to be a trade-off relationship between the size of the unit elements and the cut-off frequency, that is to say, the unit element size increases the lower the cut-off frequency is designed.
Japanese Patent Laid-Open No. 2008-288770 discloses a technique for achieving both a reduction in the size of the EBG structure and the lowering of the cut-off frequency. In the technique disclosed in Japanese Patent Laid-Open No. 2008-288770, the size of the EBG structure is reduced using multiple chip inductors or chip capacitors. However, this configuration requires the number of electronic components to be increased by the number of patch structures, thus leading to the problem of an increase in manufacturing cost. There has also been the problem of difficulty in obtaining a desired cut-off frequency due to the electronic components having frequency characteristics rather than ideal characteristics.
The present invention has been achieved in light of the above-described circumstances, and an object of an aspect of the present invention is to provide an electromagnetic band gap structure that is small and whose cut-off frequency is adjustable.